The spectrophotometric determination of trace amounts of iron and cobalt was investigated for flow injection analysis. Cationic or polarized metal chelates were concentrated on a Teflon surface, which was treated with a 2 M NaOH solution for 3 hours. Then, the metal chelates adsorbed in the Teflon capillary tube were eluted with a solvent mixture of ethanol and 0.1 M HNO
3, and determined by on-line by spectrophotometry. Cobalt (III) reacted with tridentate ligands to form stable chelate complexes, which have cationic charge in the complexes. 2-(5-Bromo-2-pyridylazo)-5-[
N-n-propyl-
N-(3-sulfopropyl)amino]aniline, sodium salt (5-Br-PSAA) and 1-(2-pyridylazo)-2-naphtol (PAN) were used to form cationic complexes as tridentate and mono valence ligands. The composition of the complexes obtained under the standard conditions was metal : ligand=1 : 2. The metal complexes were concentrated for 10 min with 2.9 ml/min as the flow rate of the sample solution. As a result, the apparent molar absorption coefficients of the complexes were enhanced to 100 times as compared to each of there molar absorption coefficients. The optimum conditions were as follows: chelate complex preparation pH, 4.7; concentration pH, 8.9; eluent flow rate, 0.7 ml/min; measurement wavelength, 602 nm (Co-5-Br-PSAA), 554 nm (Fe-5-Br-PSAA), and 585 nm (Co-PAN), concentration tube length, 6 m. The cobalt was determined over the range 0.6∼50 ppb with PAN and 0.3∼10 ppb with 5-Br-PSAA; iron (III) was 0.1∼10 ppb with 5-Br-PSAA. The result of determination of iron (III) in tap water showed good agreement with the values obtained by ICP-AES.
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